Commonly known local area networks (LAN) such as an Ethernet based network communicate data via packets having a set format. Control of packet traffic in a network is critical to insure balanced communication flow and efficient transmission. Such packets are sent between a source network node and a destination node over a communication medium such as coaxial cable or twisted pair wire. Each packet typically has a header that contains limited routing information, and a payload. The amount of information in the header is limited to a destination node address and is fixed for the packet. Thus, dynamic information such as the state of various network devices that could be useful for traffic control is not available during the routing of the packet.
The most common method of local area network communication is the Ethernet protocol that is a family of frame-based computer networking technologies for local area networks. The Ethernet protocol is standardized as IEEE 802.3 and defines a number of wiring and signaling standards for the physical layer, through means of network access at the Media Access Control (MAC)/Data Link Layer, and a common addressing format.
The combination of the twisted pair versions of Ethernet for connecting end systems to the network, along with the fiber optic versions for site backbones, is the most widespread wired LAN technology. Ethernet nodes communicate by sending each other data packets that are individually sent and delivered. Each Ethernet node in a network is assigned a 48-bit MAC address. The MAC address is used both to specify the destination and the source of each data packet in the header. Network interface cards (NICs) or chips on each node normally do not accept packets addressed to other Ethernet nodes.
There have been a number of legacy Ethernet features that do not have any present application. For example, a trailer of variable size may be added to the end of an Ethernet packet according to RFC 893, and may contain information such as CRC values. Network resources may strip away the information contained in the trailer (e.g., a CRC value) and payload portions of the packet. This was standardized by RFC893 to allow certain platforms to process packets aligned on page boundaries by moving variable length header fields to the end of the packet. However, the physical layer devices still forward packets that contain an arbitrary amount of data in the trailer after the proper end of the data payload in the packet. Identifying this data requires a conceptual packet length, for example the length filed in the header of the packet. Once the payload length has been determined, any trailing data may be identified and consumed by an appropriate monitoring agent such as a receiving node. Once the packet enters the stack in the node, the node will strip off any trailing data before passing upwards to the next layer. Trailers are strictly a link level packet format and are not visible (when properly implemented) in any higher level protocol processing.